PROJECT SUMMARY/ABSTRACT Over 800,000 US adults and children are on mechanical ventilators in intensive care units each year. While major advancements in ventilator devices have improved outcomes for critically ill patients, current ventilator practice is predominately based on measurements of airway pressure. The more relevant pressure, particularly to determine if mechanical ventilation is causing harm, is the pressure across the alveoli, or transpulmonary pressure. During controlled ventilation, accurate measurements of transpulmonary pressure can help adjust ventilator settings to minimize ventilator induced lung injury, which leads to multiple organ failure, inability to wean from mechanical ventilation and death. Accurate transpulmonary pressure measurements require an estimate of pleural pressure, which is not feasible to measure directly in humans. Esophageal pressure is an accepted surrogate for pleural pressure, with esophageal balloon catheters serving as the most commonly used method for measurement. Recent research in both adults and children highlight many potential benefits of measuring esophageal pressure, but these measurements are often limited to research centers that have developed expertise in using esophageal balloon catheters. Balloon catheters have many limitations related to placement, dependence on balloon filing volume, cardiac artifact, and patient size and position. Hypothesis: We hypothesize an easier to use, more accurate, and more stable pressure sensing catheter can be made using a fiber optic pressure sensor integrated with a feeding tube. Providing an easy to use, stable and accurate pressure sensing catheter that can remain in the patient for weeks at a time and be used for feeding will increase the number of patients who will benefit from esophageal pressure measurements. Specific Aims: Rush River Research (RRR) Corporation proposes to develop a novel catheter to provide simultaneous esophageal pressure, esophageal temperature, and feeding for use in ventilated patients. In aim 1, we will develop 5-10 prototype catheters with integrated pressure sensor, temperature sensor and feeding tube which meet FDA standards for mechanical efficiency. In aim 2, we will evaluate the catheter?s accuracy in simulated pleural pressure measurement and determine the frequency with which ex-vivo calibration is needed, using a laboratory model. Aim 3 will test the catheter?s responsiveness to real changes in pleural pressure and determine if it is robust against common sources of artifact, using an animal model. Team: RRR has assembled a highly qualified team of critical care researchers and a major OEM catheter developer and manufacturer to achieve these goals.